This application is related to electrical power conversion, and in particular is related to converting and combining electrical power from multiple sources, including sources having different electrical characteristics, e.g., different frequencies and/or voltages, including DC voltages, into one or more selectable voltages at a selectable frequency or DC. In one aspect, this disclosure more particularly relates to a power converter system and method for converting electrical power of possibly different frequencies and/or voltages to different electrical power forms suitable for a variety of uses including, for example, electrical conversion useful in shipboard, ground-based, or airplane-based applications.
These uses include converting dock power for shipboard use, such as with yachts, cruise or transport ships, or military vessels for example. This disclosure also has further application to converting power for aircraft ground power systems, or transportable military or commercial ground-based systems, e.g., radar, missile batteries, or electronic warfare equipment.
One problem facing the international yachting community in particular and the international maritime community in general, is the incompatibility of dockside power with on-board ship's power requirements. For example, 60 Hertz (Hz) electrical power is widely used in North America, Japan, and parts of Africa, while 50 Hz electrical power predominates in portions of South America, Europe, and Australia. Further adding to this incompatibility is the wide variety of voltages provided at various locations throughout the world, e.g., 200, 220, 230, 240, 380, 400, 415, 460, or 480 volts (V), and the use of either single or multi-phase electrical AC power. Typically, in order to reduce expense and the types of equipment necessary on board the ship, one type of AC electrical power is often used, e.g., either 50 or 60 Hz, at a particular output voltage or voltages. In addition, 400 Hz electrical power is oftentimes used in shipboard environments for specialized electronics applications.
Further problems are encountered with instability of shore power provided to a docked ship, in that voltage and/or frequency fluctuations from the shore power supply often cause so-called “voltage sag” or “brown out” conditions, which can cause damage to electrical motors and sensitive electronic equipment due to low voltage conditions or frequency shifts.
Additional problems are encountered with “dirty” dockside power, which might be susceptible to a wide variety of electrical noise such as voltage spikes, sags, surges, or harmonic distortion which also can adversely affect sensitive onboard electronic equipment.
In the absence of a system and method to convert any commercially available voltage and/or frequency power source into a form which is compatible with fixed on-board voltage/frequency equipment, generator sets, i.e., a prime mover such as a diesel engine turning an electrical generator, must be continuously run while dockside to provide shipboard electrical power. The running of generator sets causes noise, pollution, and excessive use of fuel, even when some type of shore power is present, but unusable due to different shipboard voltage requirements. Further, light loading of a generator while dockside may also create conditions which have an adverse effect on the efficiency of the prime mover.
In one conventional approach, power converters for multiple input power supplies have been coupled through associated converters to a single load, with power factor correction and power conversion conducted for each converter. Single phase AC and DC batteries have been used to provide electrical power to a load, as well as three phase AC power inputs.
In another conventional approach, proportional conversion of power from two sources has been accomplished in single phase, 110 VAC circuits by balancing current in each converter to keep the current in each branch below a threshold which will trip a breaker. Power from two separate AC power sources having the same characteristics goes through separate AC transforming circuits and rectifiers, and power factor correction has been applied in each branch. A control circuit and regulating circuit between each circuit branch controls how the total input power from the two branches is proportionally combined and applied to the load, in response to the total power withdrawn from the two power sources, and the current passing through the two circuit branches. Currents are then always balanced, thereby reducing the possibility of one circuit branch overloading and tripping a circuit breaker.
In yet another conventional approach, a marine power distribution arrangement for supplying drive power to a ship or marine vessel propulsion motor uses multiphase, multi-circuit generators to supply isolated outputs on a plurality of lines at 50/60 Hz or at frequencies greater than 50/60 Hz. The outputs may include DC and AC outputs of variable frequency, variable voltage, and variable phase.
However, none of the conventional approaches known by the present inventor disclose, teach, or suggest combining input power sources with different frequencies or voltage characteristics, including a variety of DC input voltages, with subsequent conversion of the combined power into an AC output voltage of a selectable frequency, or into a DC output voltage at a selectable level.
What is needed then, is a system and method capable of combining power sources having different electrical characteristics such as frequency and/or voltage, and providing one or more output voltages with desired frequency, voltage, and/or phase characteristics.
What is further needed is a system and method capable of receiving “dirty” shore power from multiple sources, possibly with different electrical characteristics, and converting such “dirty” electrical power into a stabilized and conditioned electrical power in a selectable form suitable for the end user.
What is still further needed is a system and method capable of ground or air transportability and which converts a variety of input voltages into a selectable form suitable for the end user.